下面是一些关于打印list组件的例子:

public class ListExample {

    public static void main(String[] args) {
        List<Model> models = new ArrayList<>();

        // TODO: First create your model and add to models ArrayList, to prevent NullPointerException for trying this example

        // Print the name from the list....
        for(Model model : models) {
            System.out.println(model.getName());
        }

        // Or like this...
        for(int i = 0; i < models.size(); i++) {
            System.out.println(models.get(i).getName());
        }
    }
}

class Model {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

列表中的对象必须实现toString，以便将有意义的内容打印到屏幕上。

下面是一个快速测试，可以看出区别:

public class Test {

    public class T1 {
        public Integer x;
    }

    public class T2 {
        public Integer x;

        @Override
        public String toString() {
            return x.toString();
        }
    }

    public void run() {
        T1 t1 = new T1();
        t1.x = 5;
        System.out.println(t1);

        T2 t2 = new T2();
        t2.x = 5;
        System.out.println(t2);

    }

    public static void main(String[] args) {        
        new Test().run();
    }
}

当它执行时，打印到屏幕的结果是:

t1 = Test$T1@19821f
t2 = 5

因为T1没有重写toString方法，所以它的实例T1输出的结果不是很有用。另一方面，T2重写了toString，所以我们控制了它在I/O中使用时打印的内容，我们在屏幕上看到了一些更好的东西。

java 11问题的解决方案是:

String separator = ", ";
String toPrint = list.stream().map(o -> String.valueOf(o)).collect(Collectors.joining(separator));

System.out.println(toPrint);

用于String数组的列表

list.forEach(s -> System.out.println(Arrays.toString((String[]) s )));

我也遇到过类似的问题。我的代码:

List<Integer> leaveDatesList = new ArrayList<>();

.....inserted value in list.......

方法1:在for循环中打印一个列表

for(int i=0;i<leaveDatesList.size();i++){
    System.out.println(leaveDatesList.get(i));
}

方法2:在forEach中打印列表，for循环

for(Integer leave : leaveDatesList){
    System.out.println(leave);
}

方法3:在java 8中打印列表

leaveDatesList.forEach(System.out::println);

You haven't specified what kind of elements the list contains, if it is a primitive data type then you can print out the elements. But if the elements are objects then as Kshitij Mehta mentioned you need to implement (override) the method "toString" within that object - if it is not already implemented - and let it return something meaning full from within the object, example: class Person { private String firstName; private String lastName; @Override public String toString() { return this.firstName + " " + this.lastName; } }